1. Field of the Invention
The present invention relates to a liquid crystal apparatus and a method of producing the same and, more particularly, to a liquid crystal apparatus using a bend alignment mode that can realize a high-speed response and a method of producing the same.
2. Description of the Related Art
In general, various alignment modes of liquid crystal have been used for a liquid crystal device depending on the intended use. For example, a Twisted Nematic (TN) mode, a Vertical Aligned (VA) mode, an In Plane Switching (IPS) mode, and an Optically Compensated Bend (OCB) mode are well known. These liquid crystal alignment modes may be determined depending on the physical property of a liquid crystal composition and the characteristics of an alignment film.
In recent years, in order to display a moving picture, a liquid crystal apparatus that has a high-speed response has been actively developed. In particular, the OCB mode has attracted attention, because the OCB has a high-speed response.
During the OCB mode, a liquid crystal alignment state that is called bend alignment is used at the time of a display operation. However, in order to form the bend alignment, an alignment transition from splay alignment of an initial alignment state becomes necessary. For this alignment transition, a transition voltage larger than or equal to a predetermined voltage is needed. If the transition voltage is increased, the driving voltage of the liquid crystal device is increased. Accordingly, the transition voltage is preferably maintained as low as possible.
It is known that in general, it is effective to increase a pretilt angle of liquid crystal layer and decrease an elastic constant (K33/K11) of a liquid crystal composition in order to decrease the transition voltage. In particular, if the pretilt angle is set to 40° or more, the transition voltage becomes unnecessary. As a result, the bend alignment can be formed without the alignment transition from the splay alignment state.
Meanwhile, if the pretilt angle is set to a high value, it is likely to generate the bend transition. However, there is posed a problem that the retardation of the liquid crystal layer is lowered, whereby the light utilization efficiency is lowered. In order to solve this problem, a technology for easily realizing a bend alignment transition even eat a low pretilt angle has been reported.
In Japanese Patent Application Laid-Open No. 2007-017502, a region where a plurality of pretilt angles are implemented is formed in a substrate plane. Specifically, a low pretilt angle region is surrounded by a high pretilt angle region to improve the ease with which the splay/bend alignment transition is generated.
The above-mentioned patent document discloses a method of forming a low pretilt angle region. According to this method, after a high pretilt angle region is formed on a substrate using an oblique deposition method where a deposition angle is 80°, a deposition region is restricted to only a pixel region using a mask, the substrate is rotated by 90° to change a deposition direction by 90°, and an oblique deposition film is formed at a deposition angle of 60°. By using this method, the pixel region comes to have a low pretilt angle by using a deposition angle of 60°, and an inter-pixel region comes to have a high pretilt angle by using a deposition angle of 80°. Furthermore, in the case of the deposition angles of 60° and 80°, an azimuthal direction, that is, liquid crystal alignment of a substrate in-plane direction, is rotated by 90°. In the above-mentioned patent document, since the deposition directions of the deposition angles of 60° and 80° are changed by 90°, the alignment orientations thereof are the same.
US Published Application No. 2006-0203171 discloses a method in which a notch portion is provided in a pixel electrode to change an electric field direction at the periphery of the notch portion, thereby forming a transfer nucleus of a splay/bend alignment transition.
Japanese Patent Application Laid-Open No. 2000-330141 discloses a method in which ultraviolet rays irradiate only a pixel region using a polyimide alignment film, where a pretilt angle is changed by ultraviolet irradiation, thereby setting a pretilt angle of the pixel region to be lower than a pretilt angle of an inter-pixel region.
However, if this method is used in a device where an alignment film is stacked in a display region such that a pretilt angle of the display region is lower than that of a peripheral region, a voltage that is actually applied to a liquid crystal layer may be lowered. If the notch portion is provided in the pixel electrode, the area of the pixel electrode may be decreased, thereby lowering reflectance. Furthermore, since an organic alignment film has weak resistance against light, it is difficult to use an organic alignment film in an environment where light with high intensity is used.